Conventionally, there has been disclosed a device that detects presence or absence of a malfunction of a humidity sensor provided in an exhaust system of an internal combustion engine, for example, in Patent Literature 1. In this device, the humidity sensor is provided in the vicinity of a hydrocarbon adsorbent provided in an exhaust system. When the operation of the internal combustion engine is stopped, water in the exhaust gas remaining around the hydrocarbon absorbent adsorbs to the hydrocarbon adsorbent. Subsequently, when the hydrocarbon adsorbent is saturated with the adsorbing water, the humidity in the vicinity of the hydrocarbon adsorbent becomes a substantially constant humidity. At this time, if the humidity sensor is normal, the humidity stays within a certain range. The device of Patent Literature 1 detects presence or absence of a malfunction of the humidity sensor by the output of the humidity sensor at the time of the output of the humidity sensor becoming substantially constant after the operation of the internal combustion engine is stopped, by using the above phenomenon.
Following is a list of patent literatures which the applicant has noticed as related arts of embodiments the present invention.
Patent Literature 1: JP 2003-172192 A
Patent Literature 2: JP 2010-223179 A
Patent Literature 3: JP 2003-148135 A
Patent Literature 4: JP 2002-048010 A